/*
 * strtod.c --
 *
 *	Source code for the "strtod" library procedure.
 *
 * Copyright (c) 1988-1993 The Regents of the University of California.
 * Copyright (c) 1994 Sun Microsystems, Inc.
 *
 * Permission to use, copy, modify, and distribute this
 * software and its documentation for any purpose and without
 * fee is hereby granted, provided that the above copyright
 * notice appear in all copies.  The University of California
 * makes no representations about the suitability of this
 * software for any purpose.  It is provided "as is" without
 * express or implied warranty.
 *
 * RCS: @(#) $Id$
 */

#include "include/strtod.h"
#include <ctype.h>

#ifndef TRUE
#define TRUE 1
#define FALSE 0
#endif
#ifndef NULL
#define NULL 0
#endif

static int maxExponent = 511;	/* Largest possible base 10 exponent.  Any
				 * exponent larger than this will already
				 * produce underflow or overflow, so there's
				 * no need to worry about additional digits.
				 */
static double powersOf10[] = {	/* Table giving binary powers of 10.  Entry */
	10.,			/* is 10^2^i.  Used to convert decimal */
	100.,			/* exponents into floating-point numbers. */
	1.0e4,
	1.0e8,
	1.0e16,
	1.0e32,
	1.0e64,
	1.0e128,
	1.0e256
};

/*
 *----------------------------------------------------------------------
 *
 * strtod --
 *
 *	This procedure converts a floating-point number from an ASCII
 *	decimal representation to internal double-precision format.
 *
 * Results:
 *	The return value is the double-precision floating-point
 *	representation of the characters in string.  If endPtr isn't
 *	NULL, then *endPtr is filled in with the address of the
 *	next character after the last one that was part of the
 *	floating-point number.
 *
 * Side effects:
 *	None.
 *
 *----------------------------------------------------------------------
 */

double
p_strtod(const char * string, char **endPtr)
/* const char *string;	A decimal ASCII floating-point number,
			 * optionally preceded by white space.
			 * Must have form "-I.FE-X", where I is the
			 * integer part of the mantissa, F is the
			 * fractional part of the mantissa, and X
			 * is the exponent.  Either of the signs
			 * may be "+", "-", or omitted.  Either I
			 * or F may be omitted, or both.  The decimal
			 * point isn't necessary unless F is present.
			 * The "E" may actually be an "e".  E and X
			 * may both be omitted (but not just one).
			 */
			 /* char **endPtr;		If non-NULL, store terminating character's
						  * address here. */
{
	int sign, expSign = FALSE;
	double fraction, dblExp, *d;
	register const char *p;
	register int c;
	int exp = 0;		/* Exponent read from "EX" field. */
	int fracExp = 0;		/* Exponent that derives from the fractional
				 * part.  Under normal circumstatnces, it is
				 * the negative of the number of digits in F.
				 * However, if I is very long, the last digits
				 * of I get dropped (otherwise a long I with a
				 * large negative exponent could cause an
				 * unnecessary overflow on I alone).  In this
				 * case, fracExp is incremented one for each
				 * dropped digit. */
	int mantSize;		/* Number of digits in mantissa. */
	int decPt;			/* Number of mantissa digits BEFORE decimal
				 * point. */
	const char *pExp;		/* Temporarily holds location of exponent
				 * in string. */

				 /*
				  * Strip off leading blanks and check for a sign.
				  */
	if (!string) {
		return 0;
	}
	p = string;
	while (isspace(*p)) {
		p += 1;
	}
	if (*p == '-') {
		sign = TRUE;
		p += 1;
	}
	else {
		if (*p == '+') {
			p += 1;
		}
		sign = FALSE;
	}

	/*
	 * Count the number of digits in the mantissa (including the decimal
	 * point), and also locate the decimal point.
	 */

	decPt = -1;
	for (mantSize = 0; ; mantSize += 1)
	{
		c = *p;
		if (!isdigit(c)) {
			if ((c != '.') || (decPt >= 0)) {
				break;
			}
			decPt = mantSize;
		}
		p += 1;
	}

	/*
	 * Now suck up the digits in the mantissa.  Use two integers to
	 * collect 9 digits each (this is faster than using floating-point).
	 * If the mantissa has more than 18 digits, ignore the extras, since
	 * they can't affect the value anyway.
	 */

	pExp = p;
	p -= mantSize;
	if (decPt < 0) {
		decPt = mantSize;
	}
	else {
		mantSize -= 1;			/* One of the digits was the point. */
	}
	if (mantSize > 18) {
		fracExp = decPt - 18;
		mantSize = 18;
	}
	else {
		fracExp = decPt - mantSize;
	}
	if (mantSize == 0) {
		fraction = 0.0;
		p = string;
		goto done;
	}
	else {
		int frac1, frac2;
		frac1 = 0;
		for (; mantSize > 9; mantSize -= 1)
		{
			c = *p;
			p += 1;
			if (c == '.') {
				c = *p;
				p += 1;
			}
			frac1 = 10 * frac1 + (c - '0');
		}
		frac2 = 0;
		for (; mantSize > 0; mantSize -= 1)
		{
			c = *p;
			p += 1;
			if (c == '.') {
				c = *p;
				p += 1;
			}
			frac2 = 10 * frac2 + (c - '0');
		}
		fraction = (1.0e9 * frac1) + frac2;
	}

	/*
	 * Skim off the exponent.
	 */

	p = pExp;
	if ((*p == 'E') || (*p == 'e')) {
		p += 1;
		if (*p == '-') {
			expSign = TRUE;
			p += 1;
		}
		else {
			if (*p == '+') {
				p += 1;
			}
			expSign = FALSE;
		}
		while (isdigit(*p)) {
			exp = exp * 10 + (*p - '0');
			p += 1;
		}
	}
	if (expSign) {
		exp = fracExp - exp;
	}
	else {
		exp = fracExp + exp;
	}

	/*
	 * Generate a floating-point number that represents the exponent.
	 * Do this by processing the exponent one bit at a time to combine
	 * many powers of 2 of 10. Then combine the exponent with the
	 * fraction.
	 */

	if (exp < 0) {
		expSign = TRUE;
		exp = -exp;
	}
	else {
		expSign = FALSE;
	}
	if (exp > maxExponent) {
		exp = maxExponent;
		//errno = ERANGE;
	}
	dblExp = 1.0;
	for (d = powersOf10; exp != 0; exp >>= 1, d += 1) {
		if (exp & 01) {
			dblExp *= *d;
		}
	}
	if (expSign) {
		fraction /= dblExp;
	}
	else {
		fraction *= dblExp;
	}

done:
	if (endPtr != NULL) {
		*endPtr = (char *)p;
	}

	if (sign) {
		return -fraction;
	}
	return fraction;
}
